Killings not "in furtherance" of the felony
General Rule: If it can be shown that a killing was not in furtherance of the felony, i.e. the killing did not aid or advance the felony, the felony-murder rule does not apply.
Three Problematic Applications:
Killings after the felony has ended (Gillis)
(e.g. burglar may be involved in a fatal accident after he has successfully made his getaway)
Outcome: Generally, the felony-murder rule may not apply where the killing occurs after the felony has ended. However, there are complications involved in determining when a felony ends.
Killings by cofelons but not in furtherance (Heinlein)
(e.g. one of two men planning to commit arson may, while en route to the fire, rob someone and accidentally kill him; co-felon has gone off on "a frolic of his own.")
Outcome: Generally, the felony-murder rule may not apply where the killing is not in furtherance of the felony, regardless of whether it is committed by the felon, or by a cofelon.
Killings by nonfelons (Canola)
(e.g. a police officer or a victim resisting a robbery may fire a shot that kills a co-felon or an innocent bystander)
Agency: the doctrine of felony-murder does not extend to a killing, although growing out of the commission of the felony, if directly attributable to the act of one other than the defendant or those associated with him in the unlawful enterprise. (adopted by the court in Canola)
Proximate Cause: felony-murder applies for any death proximately resulting from the unlawful activity, regardless of who kills who